1. Field of the Invention
The present invention relates to a device having an element that is comprised of a luminous material sandwiched between electrodes (hereinafter referred to as luminous element) (hereinafter the device will be referred to as light emitting device) and to a method of manufacturing the same. In particular, the present invention relates to a light emitting device using a luminous element that utilizes a luminous material (hereinafter referred to as an EL material) which provides EL (Electro Luminescence) (hereinafter the luminous element will be referred to as an EL element and the device will be referred to as an EL light emitting device). It is to be noted that an organic EL display and an organic light emitting diode (OLED) are included in the light emitting device of the present invention.
Further, the EL materials that can be used in the present invention include all the EL materials that luminesce by way of a singlet excitation or a triplet excitation, or via both excitations (fluorescence and/or phosphorescence).
2. Description of the Related Art
The EL light emitting device is constructed of a structure having an EL element that is composed of an anode, a cathode, and an EL material sandwiched therebetween. By applying a voltage between the anode and the cathode to cause a current to flow in the EL material, the carriers are made to re-couple, whereby the EL element emits light. In other words, the luminous element itself in the EL light emitting device has a luminescing ability, and therefore the EL light emitting device, unlike a liquid crystal display device, does not need a back light. In addition, the EL light emitting device has merits such as a wide angle of view and is light in weight.
At this point, when film deposition is performed on the EL material to thereby form the EL layer, various types of film deposition methods are adopted. In particular, the evaporation method is employed for the film deposition of a low molecular weight type organic EL material, while the spin coating method or the ink jet method is employed for film deposition of a high molecular weight type organic EL material.
In any case, although there are strong points and shortcomings in all the film deposition methods, there exist a problem in the case of the evaporation method where the utilization of EL material is inefficient. In the case of the evaporation method, the EL material is formed by being vaporized through resist heating or electron beam heating and then scattered. However, the amount of loss due to the EL material being formed on areas other than on the surface to be formed, such as on an evaporation mask (shadow mask) and on the interior of the evaporation chamber, was large. The price of the EL material in the present situation is high, and hence, this type of problem consequently invites an increase in the manufacturing costs.
Further, in the case of the ink jet method, the tracks of the drops of solution containing the EL material that is discharged from the tip end of a nozzle is difficult to control, thereby making it difficult to accurately control the point where the drops of solution is to be applied (the portion where the EL layer is to be formed). If the application point is off the point, a problem in which the drops of solution will mix into an adjacent pixel may occur. This problem, in particular, becomes particularly a conspicuous problem in terms of manufacturing a light emitting device having a highly definite pixel portion.
The present invention has been made in view of the above problem, and therefore an object of the present invention is to provide a technique for accurately controlling a film deposition position in forming an EL material. Another object of the present invention is to attain a light emitting device that has a highly definite pixel portion. A further object of the present invention is to provide an electric appliance, which has high displaying quality, that employs the light emitting device as its display portion.
The present invention is characterized in that a metal film is used for forming a portion of a bank for dividing the pixels, and then a voltage is applied to the metal film (to make a negative or positive charge) to form an electric field to thereby control a track of the EL material. Therefore, in this specification, xe2x80x9capplying an electric fieldxe2x80x9d means xe2x80x9ccontrolling the direction of the charged particlesxe2x80x9d.
It is to be noted that the term xe2x80x9cbankxe2x80x9d throughout this specification, indicates a lamination layer that is composed of an insulating film and a conductive film and provided so as to surround a pixel electrode. The bank assumes the role of dividing the respective pixels. In addition, for the sake of convenience in making the present invention clear, the bank is divided into parts and classified as xe2x80x9ca supporting bankxe2x80x9d and xe2x80x9ca controlling bankxe2x80x9d throughout this specification.
By adopting the above-mentioned structure, in film deposition methods such as the evaporation method, the ion plating method, or the ink jet method in which the discharged EL material adheres to the upper part or the lower part of the surface on which the EL material is to be formed, it is possible to accurately control the film deposition position of the EL material. As a result, a light emitting device having a highly definite pixel portion can be attained.